This application is based on Japanese Patent Application No. 2001-323598 filed on Oct. 22, 2001, the disclosure of which is incorporated herein by reference.
The present invention relates to a rotary electric machine mounted on vehicles, aircraft and the like.
A vehicular alternating current generator is required to be compact, light weight, high power and high performance, to improve fuel efficiency of a vehicle. As a means of improving power output, for example, a multi-poles single field winding type rotor, what is called a Lundell-type field rotor, is known. In the Lundell-type rotor, a field winding is concentrically wound around a core on a rotor shaft so that a large magnetomotive force is supplied to each pole of a stator.
The Lundell-type field rotor is an eternal art. The Lundell-type field rotor has been begun to use from 1903s in commercial power stations such as in Germany. Recently, it is used just in a field of such as automobile requiring downsizing, high-power generation and weight reduction. In the background, there is difficulty in improving power generation efficiency in a power generator having the Lundell-type rotor.
For example, solid magnetic poles cause large iron loss due to magnetic flux fluctuation caused during transfer between the rotor and a stator core. Also, because it is difficult to form a fine magnetic pole surface corresponding to a cosine function curve, the magnetic pole surface becomes a cylindrical surface. Even when it is formed into a trapezoidal magnetic pole form to provide salient pole form efficiency, it tends to increase a magnetic flux passing through the stator core. Therefore, it is still difficult to decrease iron loss. Further, it is difficult to suppress armature reaction.
The present invention is made in view of the above disadvantages, and it is an object of the present invention to improve power generation efficiency in a rotary electric machine having a Lundell-type field winding rotor.
According to an aspect of the present invention, a rotary electric machine has a stator and a rotor. In the stator, multi-phase windings are wound around a stator core. The rotor is provided radially inside the stator core. The rotor has a cylindrical boss press-fit around a rotor shaft, disc portions extending radially outward from the boss, claw pieces connected with the disc portions radially outside the boss, and a field winding located between the boss and the claw pieces. Also, the rotor has an annular core radially outside the claw pieces. The annular core is made of a stack of annular steel sheets and has slits formed in the radial direction.
Since the annular core is provided radially outside the claw pieces, iron loss is decreased. Further, since the annular core has slits formed in the radial direction, leaks of magnetic fluxes from the claw pieces are suppressed with the slits. Accordingly, power generation efficiency of the rotary electric machine having the Lundell-type rotor can be improved.